(1) Field of the Invention
The present invention belongs to the technical field of image forming apparatus in which an image is formed by conveying a predetermined recording medium along a plurality of image supports arranged in parallel to each other so as to sequentially and superimposingly transfer the developed images on individual image supports to the recording medium. More detailedly, the present invention relates to an image forming apparatus of the so-called tandem type having a plurality of image supports each having a rotational inertial body such as a flywheel or the like at one end of their rotary shafts.
(2) Description of the Prior Art
In general, in conventional image forming apparatus for recording designated image information by performing line-wise scanning such as laser scanning on an image support such as a phtoreceptor, drive irregularity occurs in the driving mechanism for rotating the image support. When an image of lines is recorded, this drive irregularity will cause image unevenness (so-called banding) which is made up of bands in the final image on the recording medium.
In order to solve the above problem, a rotating inertial body such as a flywheel has been provided at one end of the rotary shaft of the image support. That is, in an attempt to reduce the drive irregularity originating from the driving mechanism, a heavy, rotating inertial body has been provided to produce the desired inertia for the rotation of the image support.
On the other hand, in the field of image forming apparatus, there has been a development towards multil-colorization of recorded images. A known typical example of color image forming apparatus is the so-called tandem type having multiple image supports therein. In such a color image forming apparatus, when a developed image of a relatively more visible color on the image support deviates from the correct position due to drive irregularity, color blur occurs in each developed image even if the deviation is slight. Therefore, it is necessary to establish rotational synchronism between individual image supports, so that rotational inertial bodies of an identical type need to be provided for all the multiple, image supports in order to take into account the rotational drive irregularity of the image supports.
Accordingly, in an image forming apparatus having multiple image supports, provision of rotational inertial bodies of an identical type for all the multiple image supports increases the number of assembly parts, hence causing various problems including: lowering of design flexibility, increase in the manufacturing cost, making the apparatus bulky hence the needing of a large space for installation, and increase in the machine weight hence rise in the cost for transportation.
Japanese Patent Application Laid-Open Hei 4 No.147279 has proposed a technique that reliably establishes synchronized rotations of all the image supports in an image forming apparatus of the so-called tandem type while preventing bulkiness of the apparatus. That is, in this configuration, the rotational inertial bodies are made up of an non-circular shape having the same inertia and attached on the rotational shafts of all the image supports to thereby reduce the distance between image supports.
As above, in the tandem type, image forming apparatus of Japanese Patent Application Laid-Open Hei 4 No.147279, the rotational inertial bodies provided on the rotational shafts of all the image supports, have the same, non-circular sectional feature in order to equally increase the inertia of all the image supports, whereby it is possible to reduce the distance between image supports, and hence this configuration contributes to securing reliable synchronized rotations of multiple image supports whilst minimizing the size of the image forming apparatus.
It is true that the technology described above can shorten the distance between image supports and inhibit the bulkiness of the apparatus as a whole, compared to the conventional configuration where circular rotational inertial bodies are arranged in parallel, but it still suffers from unsolved problems of increase in the manufacturing cost and apparatus weight due to increase in the number of assembly parts since the rotational inertial bodies of the same type are needed for all the image supports. Further, this configuration is limited by the complex shape of the rotational inertial bodies and their arrangement and also by the necessity of a control means and the like for exactly controlling the rotational positions of the rotational inertial bodies so as not to interfere with each other. Thus, there are sill unsolved problems such that design flexibility is markedly hindered.